There is an increasing industrial and societal need for safer and more environmentally-friendly ingredients and methods for preparing those ingredients. In particular, it is highly desirable to provide methods that reduce or eliminate the use of irritating or allergenic starting materials, that employ biocompatible reagents, and that optimally use starting materials derived from a natural source or are “nature-equivalent.” This is of urgent interest in consumer-facing industries, such as personal and household care.
One class of materials that may be approached in a “greener” manner is surfactants. Specifically, there is a need for new amphoteric surfactants that avoid using irritating or allergenic starting materials and that are made in a more environmentally-friendly manner.
Amphoteric (or zwitterionic) surfactants are used throughout the personal and household care industries. They are classified as specialty co-surfactants that complement the performance of primary surfactants. These co-surfactants also increase the mildness of the formulation by reducing irritation associated with purely ionic surfactants.
The most common zwitterionic sulfonate surfactants are amido-amine based materials produced by a multi-step process from coconut or palm kernel oil and N,N-dimethylamino-3-propylamine (DMAPA). Various patents (U.S. Pat. Nos. 3,280,179; 4,259,191) and publications (Parris et al., J. Am. Oil Chem. Soc., Vol. 54, pp. 294-296 (1977)) detail commonly used preparation methods for these types of materials. The processes generally involve the amidation of fatty acids with DMAPA at high temperatures (150-175° C.). The intermediate fatty amino-amide is then reacted with a hydrophilic species, e.g., propane sultone or sodium 3-chloro-2-hydroxypropanesulfonate, to yield the final zwitterionic surfactant.
These processes have several drawbacks. For example, typical amidation processes require high temperatures for conversion and distillation to remove unreacted starting materials. These high reaction temperatures can generate by-products and impart color to the products, requiring additional steps to remove the by-products and the color.
Moreover, DMAPA is a known sensitizer, as is the corresponding amido-amine. Both are found in trace quantities in the final formulation.
Thus, there is a need for amphoteric/zwitterionic surfactants that can be prepared under milder conditions and without the use of DMAPA or a DMAPA amide.
The present invention addresses this need as well as others, which will become apparent from the following description and the appended claims.